In [1]}, the author showed that the algebras of partial functions of signature \((\circ ,\sqcup ,-)\)  are axiomatised as the class of right-handed skew Boolean algebras. It follows that the axioms given in Proposition REF  for minus-algebras with override must be equivalent to the rather more complex axioms for right-handed skew Boolean algebras (something we have verified directly using Prover9). The result in [1]} was published prior to the axiomatisation of the functional signature \((\circ ,\sqcup )\)  as right normal distributive symmetric skew lattices given in [3]} by the same author; we have just shown that one can easily obtain the richer axiomatisation involving minus from the one without it.
